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接口可以聲明事件。 下面的示例演示如何在類中實現接口事件。 這些規則基本上都與實現任何接口方法或屬性時的相同。
在類中實現接口事件
在類中聲明事件，然后在相應區域中調用它。
namespace ImplementInterfaceEvents
{
public interface IDrawingObject
{
event EventHandler ShapeChanged;
}
public class MyEventArgs : EventArgs
{
// class members
}
public class Shape : IDrawingObject
{
public event EventHandler ShapeChanged;
void ChangeShape()
{
// Do something here before the event…
OnShapeChanged(new MyEventArgs(/*arguments*/));
// or do something here after the event.
}
protected virtual void OnShapeChanged(MyEventArgs e)
{
ShapeChanged?.Invoke(this, e);
}
}
}示例
下面的示例演示如何處理不太常見的情況：類繼承自兩個或多個接口，且每個接口都具有相同名稱的事件。 在這種情況下，你必須為至少其中一個事件提供顯式接口實現。 為事件編寫顯式接口實現時，還必須編寫 add 和 remove 事件訪問器。 通常這些訪問器由編譯器提供，但在這種情況下編譯器不提供它們。
通過提供自己的訪問器，可以指定兩個事件是由類中的同一個事件表示，還是由不同事件表示。 例如，如果根據接口規范應在不同時間引發事件，可以在類中將每個事件與單獨實現關聯。 在下面的示例中，訂閱服務器確定它們通過將形狀引用轉換為 IShape 或 IDrawingObject 接收哪個 OnDraw 事件。
namespace WrapTwoInterfaceEvents
{
using System;
public interface IDrawingObject
{
// Raise this event before drawing
// the object.
event EventHandler OnDraw;
}
public interface IShape
{
// Raise this event after drawing
// the shape.
event EventHandler OnDraw;
}
// Base class event publisher inherits two
// interfaces, each with an OnDraw event
public class Shape : IDrawingObject, IShape
{
// Create an event for each interface event
event EventHandler PreDrawEvent;
event EventHandler PostDrawEvent;
object objectLock = new Object();
// Explicit interface implementation required.
// Associate IDrawingObject's event with
// PreDrawEvent
#region IDrawingObjectOnDraw
event EventHandler IDrawingObject.OnDraw
{
add
{
lock (objectLock)
{
PreDrawEvent += value;
}
}
remove
{
lock (objectLock)
{
PreDrawEvent -= value;
}
}
}
#endregion
// Explicit interface implementation required.
// Associate IShape's event with
// PostDrawEvent
event EventHandler IShape.OnDraw
{
add
{
lock (objectLock)
{
PostDrawEvent += value;
}
}
remove
{
lock (objectLock)
{
PostDrawEvent -= value;
}
}
}
// For the sake of simplicity this one method
// implements both interfaces.
public void Draw()
{
// Raise IDrawingObject's event before the object is drawn.
PreDrawEvent?.Invoke(this, EventArgs.Empty);
Console.WriteLine("Drawing a shape.");
// Raise IShape's event after the object is drawn.
PostDrawEvent?.Invoke(this, EventArgs.Empty);
}
}
public class Subscriber1
{
// References the shape object as an IDrawingObject
public Subscriber1(Shape shape)
{
IDrawingObject d = (IDrawingObject)shape;
d.OnDraw += d_OnDraw;
}
void d_OnDraw(object sender, EventArgs e)
{
Console.WriteLine("Sub1 receives the IDrawingObject event.");
}
}
// References the shape object as an IShape
public class Subscriber2
{
public Subscriber2(Shape shape)
{
IShape d = (IShape)shape;
d.OnDraw += d_OnDraw;
}
void d_OnDraw(object sender, EventArgs e)
{
Console.WriteLine("Sub2 receives the IShape event.");
}
}
public class Program
{
static void Main(string[] args)
{
Shape shape = new Shape();
Subscriber1 sub = new Subscriber1(shape);
Subscriber2 sub2 = new Subscriber2(shape);
shape.Draw();
// Keep the console window open in debug mode.
System.Console.WriteLine("Press any key to exit.");
System.Console.ReadKey();
}
}
}
/* Output:
Sub1 receives the IDrawingObject event.
Drawing a shape.
Sub2 receives the IShape event.
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